Abstract
The European Student Earth Orbiter (ESEO) is a micro-satellite mission to Low Earth Orbit and is being developed, integrated, and tested by European university students as an ESA Education Office project. AMSAT-UK and Surrey Space Centre are contributing to the mission with a transceiver and transponder similar to that of FUNcube-1 with the addition of utilising an Atmel AT32 processor for packet software-redundancy, baseband processing, forward error correction, and packet forming; acting as a step towards software defined radio using automotive microprocessors [1]. As on the FUNcube-1 satellite, the telemetry formats and encoding schemes presented utilize a large ground network of receivers on the VHF downlink and conforms to 1200 bps and a new 4800 bps redundant downlink for the rest of the spacecraft. The uplink is on L-band using bespoke partial-CCSDS frames.
This paper describes the lean satellite design approach introduced by Cho et al. [2] for hardware and software development and testing of the proto-flight model (PFM) payload computer. Furthermore, it assesses the compliance of the project to customer and ESA specifications and discusses the applicability of these standards. Finally, lessons learned are elaborated to provide guidance for future small satellite projects. Through multiple student projects, it was possible to successfully develop a proto-flight model using the lean satellite design approach which entailed an improvement of customer specification compliance from 81% to 86% comparing to the engineering model.
In software, utilising the Google Test Suite for verification of the SDR functions and FreeRTOS tools allowed students to optimize processor load margins to 30% when operating parallelized ADC and DAC, and CAN-open telemetry chains and exploring stable memory operations. A further finding was that in Summer 2017, there was an overall compliance of 82% to the CubeSat standard and 57% to the analysed set of ECSS specifications could be achieved. The poorer compliance in ECSS is due to the incomplete environmental testing at that time. The unfunded and student-based nature of the project places significant challenges when compared to conventional missions – but this was outweighed by the ESEO flight opportunity. Following this, we recommended to further the development of a new ISO standard for lean satellite design as initiated by Cho et al. [3] which eases the development process and reliability of small space projects that struggle to fully comply to ECSS or CubeSat specifications. ESA have since defined a subset of ECSS Specifications for educational and CubeSat missions.